1. Field
This invention relates to levelling devices and, more particularly, to such devices used for permanent installation between a structural frame member, such as in a mobile home, and the supporting foundation, especially when the foundation rests on uneven terrain.
2. Description of the Prior Art
Lifting and levelling devices utilizing a pair of slidable wedges are well known. U.S. Pat. No. 3,078,072 entitled "Levelling Device for Derricks", issued Feb. 19, 1963, for example, discloses a device having a pair of wedge members with oppositely threaded holes formed therethrough. A screw shaft passes through the wedge members and engages the threaded holes, so that rotation of the shaft causes the wedge members to diverge when turned in one direction, and converge when turned in the opposite direction. Movement of the wedge members causes the lift section to move upward or downward, depending upon the direction the shaft is rotated. The device shown in the '072 patent, however, does not include any provision for accommodating non-parallel surfaces.
Russian Patent No. 623,819 published Aug. 2, 1978 to inventor Kurbatov discloses a lifting and centering device having top and base portions with inclined surfaces formed thereon, and wedge members slidably disposed therebetween. Each wedge member includes a central pivot pin having a threaded hole formed therethrough, one such hole having right hand screw threads and the other having left hand screw threads, interconnected by a central threaded shaft. As with the '072 levelling device mentioned above, rotation of the shaft causes the wedges to move in opposite directions, either converging or diverging, resulting in vertical adjustment of the device. The Russian device is also capable of accommodating misalignment between the supporting surface and structure being supported, as the top and base portions are angularly adjustable relative to one another.
The use of a rotating shaft having both left and right hand screw threads, as with the above described devices, has been found to have certain disadvantages. First, threaded rods of this nature are relatively expensive when compared to a conventional threaded rod having only right hand screw threads. Second, this arrangement requires that both wedge members move concurrently, and does not allow the user to adjust the position of one wedge member without moving the other. Additionally, the threaded pivot pins in the Russian '819 device are susceptible to dislocation in either the longitudinal or lateral direction due to the forces generated by the wedges and the threaded rod. The wedges are also susceptible to dislocation, making the device unsafe for continuous usage in permanent installations, such as beneath a mobile home.